An ink jet printing system typically includes a printhead and an ink supply which supplies liquid ink to the printhead. The printhead ejects ink drops through a plurality of nozzles and toward a print medium, so as to print an image onto the print medium. In thermal ink jet printing, heat is used to accomplish ejection of the ink. More specifically, the printhead ejects an ink drop through a nozzle by rapidly heating a small volume of ink in a chamber adjacent to the nozzle. The heating causes the ink to vaporize and be ejected from the nozzles. Heating is typically done using small electric heating elements, such as thin film resistor elements, also referred to as heating resistors. Each single printing element, or drop generator, in a printhead therefore typically includes a nozzle, a vaporization chamber, and a heating resistor.
Heating resistors can be subjected to severe mechanical stresses during thermal ink jet printing. These stresses arise in part from thermal cycling of resistors, and also from the cavitation pressures produced during the cooling phase of the ejection cycle, when the bubble of vaporized ink collapses onto the resistor surface. Such stresses can produce wear on the resistors in the form of etching, cracking, or delamination, and eventual failure of the resistor. These phenomena can be of particular significance in high ink usage printing applications, such as inkjet web press printing, retail photo printing and large format printing. Improving resistor life can be valuable to users, as ink pen replacement can be a large factor in operating costs for such applications. Printing approaches that provide increased resistor life with ink jet inks can increase the practical applications of ink jet printing.